The present invention relates to instrumental chemical analysis. More particularly, the invention relates to instrumental chemiluminescence analysis.
Chemiluminescence (CL) is the generation of light from chemical reactions. CL processes have attracted mankind""s attention for centuries. Aristotle wrote the first known report on the phenomenon when he noted weak light emitted by dead fish and fungi. The term chemiluminescence was first defined by Wiedemann in 1888 as light emitted from chemical reactions.
Many CL reactions are now well known. Early studies of CL focused primarily on the chemistry and mechanisms of CL reactions. In the early 1960""s analytical applications of CL reactions began to appear in the literature. Since then, CL analytical methods have grown substantially due to the advantages of low detection limits, wide linear dynamic ranges, and fast response.
The early analytical applications involved manual techniques for mixing reagent and sample, and measuring the light emitted. In 1975 Ruzicka and Hansen introduced Flow Injection Analysis (FIA), which provided a new tool for performing CL analyses.
With FIA, reagent and sample can be automatically mixed rapidly and reproducibly in a flowing stream in close proximity to the CL detector. Flow cell designs which caused reagent and sample to merge directly in front of the detector allowed rapid CL chemistry to be viewed. This automation made CL an even more attractive analytical technique.
In 1990 Ruzicka and Marshall introduced Sequential Injection Analysis (SIA). SIA is a variant of FIA which offers some important advantages. Whereas with FIA the sample is injected into a flowing carrier stream, with SIA adjacent sample and reagent zones are aspirated into a holding coil, and then the flow is reversed to transport the zones to the detector. Mixing and chemistry between the zones occurs during transport. SIA can be performed with simpler hardware and uses much less reagent compared to FIA.
In 1994 Tucker et al. applied SIA to CL analysis. A schematic of the system is shown in FIG. 1, and is generally designated by the numeral 2. The system 2 comprises a carrier solvent 4, a syringe pump 6, a holding coil 8, a multiport selection valve 10, a chemiluminescence flow cell 12, sample 14, reagent 76, and a detector 18. The technique provided the advantage of consumption of much less reagent 16, and generated less waste. However, since mixing and chemical reaction are initiated as sample 14/reagent 16 zones are aspirated into the holding coil 8, and continue as the flow is reversed and the reaction zone is transported to the detector 18, there is a time delay before the light-emitting zone reaches the flow cell 12 and detector 18. This delay is a disadvantage of SIA in its conventional prior-art configuration when used with rapid CL reactions.
In 1999 Dasgupta reported a liquid-core waveguide (LCW) cell for CL by FIA, and later was issued a patent on the invention. Sample and reagent are merged at the entrance of the tubular LCW. The LCW acts both as a mixing/reaction cell and a light collector. An LCW has the property that light generated within Its lumen is efficiently transmitted to both ends of the LCW. The light arriving at either end of the LCW is then measured with a suitable detector. FIA with an LCW cell has two major advantages. First, since mixing of sample and reagent occurs primarily within the LCW, CL from very fast reactions can be detected. Second, because the LCW effectively collects and transmits most of the CL emission, a high-detection sensitivity can be achieved.
In general, the present invention provides an automated chemiluminescence analyzer. The analyzer comprises (a) a multiport selection valve, (b) a bi-directional pump, (c) a flow-through chemiluminescence cell, (d) a multiport block, and (e) a detector. The multiport valve includes a common aspiration port for carrier solvent, sample, and reagent; inlet ports for sample and reagent; and an outlet port. The pump is connected to the selection valve. The chemiluminescence cell is disposed between the selection valve and the multiport block. A first end of the cell is connected to the common port of the selection valve, and a second end is connected to the multiport block. The multiport block has a first port connected to the pump, a second port which communicates with the detector, and a third port connected to the second end of the cell. The outlet port of the selection valve is constructed and arranged for discharging and flushing the cell with solvent by reversing the direction of flow through the pump.